Question can some bettas stress themself to couse finrot ,who i ask this is in some of my copper i notice signs of finrot but only on the tails and these guys show the most aggression of my males the jars they are keep in hold 2 litres i change water 2-3 times a week

Your water change routine sounds fine so it should not be dirty water causing the fin rot. Stress compromises your bettas immune system and puts them at risk of all sorts of illnesses including fin rot so to answer your question yes stress has the potential to cause fin rot.

that just as i though , couse only a few of the copper males show it and they r the most aggressive i try not to over feed them too wat would be a good meds to use to help cure it any ideas plz feel free to share